Marine Biology 59,141-149 (1980) MARINE BIOLOGY 9 by Springer-Verlag 1980 Biochemical Responses of the Striped Mullet Mugil cephalus to Oil Exposure I. Acute Responses m Interrenal Activations and Secondary Stress Responses P. Thomas*, B. R. Woodin**, and J. M. Neff Department of Biology, Texas A&M University; College Station, TX 77843, USA Abstract Acute single exposures to the water-soluble fraction (WSF) of a No. 2 fuel oil influences several biochemical parameters in juveniles of Mugil cephalus Linnaeus. Plasma cortisol and glucose concentrations were measured at 1 and 3 h after exposure to 1,5, 10 or 20% WSF. No elevation of plasma cortisol or glucose levels occurred in fish exposed to the lowest concentration of oil, whereas a dose-response relationship was observed at higher doses. The dynamics of plasma corticosteroid, glucose and cholesterol concentrations and osmolality as well as accumulation of naphthalenes in the fish tissues were monitored during exposure to 20% WSF. Circulating cortisol concentrations rose rapidly to 5 times normal values 1 h after exposure to oil and subsequently declined to control levels 6 h after oil addition. A smaller second- ary rise occurred at 12 h, but cortisol had returned to basal levels 12 h later. In contrast, plasma glucose, cho- lesterol and osmolality rose more slowly to reach maxi- mum values between 3 and 4 h after oil addition. By 24 h plasma cholesterol and osmolality had returned to normal values whereas the hyperglycemia persisted. However, 72 h after the addition of WSF all biochemical parameters had returned to control levels. At this time considerable accumulation of total naphthalenes had occurred in several fish tissues, whilst the concentration of total naphthalenes in the exposure tanks had declined to background levels. When freshly prepared 20% WSF was added to the exposure tanks during this period, all biochemical parameters were again elevated. The results suggest that the volatile components of fuel oil in the water trigger the biochemical changes described in a dose- dependent manner. The possible ecological significance of these changes and the potential use of these param- * Present address: University of Texas Marine Science Institute, Port Aransas Marine Laboratory; Port Aransas, TX 78373, USA ** Present address: Woods Hole Oceanographic Institute, Woods Hole, MA 02543, USA eters as sublethal indicators of environmental contamina- tion are discussed. Introduction The productive estuarine and coastal environments are frequently subject to contamination by petroleum. Polycyclic aromatic hydrocarbons and particularly naphthalenes and phenanthrenes are toxic and persistent in the environment (Palmork etal., 1973 ; Anderson et al., 1974a; Youngblood and Blumer, 1975; Neff et al., 1976a; Laughlin and Neff, 1979). Continuous monitoring of the marine environment is necessary in order to assess the ecological impact of petroleum discharges. Acute toxicity studies have frequently been used for this purpose. How- ever, a pollutant level which is sublethal in 96 h bioassays may nevertheless reduce the long-term viability of a population. Acceptable limits for hydrocarbon levels should therefore take into consideration the sublethal effects of oil (Wilson, 1975; Perkins, 1979). Activation of the hypothalamo-pituitary-adrenal sys- tem is a general response to environmental "stress" in mammals which represents are early stage of the general adaptation syndrome (GAS) described by Selye (1950). Corticosteroid stress responses, analogous to those of mammals, have been demonstrated in freshwater teleosts in response to several pollutants (Hill and Fromm, 1968; Lockhart et al., 1972; Donaldson and Dye, 1975). How- ever, only slight elevation of plasma cortisol levels occur- red in coho salmon exposed to cadmium (Schreck and Lorz, 1978), raising questions about the applicability of the GAS to teleosts. The purpose of the pregent study was to determine whether water-soluble fractions of petroleum cause a corticosteroid response in fish. The dose-response rela- tionships and the time course of elevated plasma cortisol levels were investigated to characterize the response further and to determine whether adaptation occurs. Adaptation in mammals is the stage during continuous 0025-3162/80/0059/0141/$01.80